The Battle of The River Isar 23 April 1809
Background
This would be the eighth battle of our campaign. A battle the Austrians would have been better advised not to fight.
Situation
Since the Battle of STRAUBING on the 19 Apr, the 1st and 2nd Armee Korps (AK) and the 2nd Reserve Armee Korps (RAK) had been withdrawing south east under increasingly heavier pressure from the French. During this retreat they had studiously kept their right flank secure by keeping close to the Danube to their North. On the 23 April the French caught them with the Austrians with their back to the River ISAR as they were trying to withdraw across it. At dawn the 2nd RAK was in the process of crossing the River ISAR with the 2nd AK in column of route next to cross, while the 1st AK were arrayed in defensive positions waiting for the order to retire.
Napoloeon had massed the III Corps D’Armee (CA) with 5 divisions, the VII (Bav) CA with 3 divisions and two Heavy Cavalry divisions and one Light Cavalry division to pursue the Austrians down the DANUBE. Of these forces the VII (Bav) CA were present on the battlefield on the 23rd April. The III CA were in line of march following and were due to arrive from 1000hrs, with the Heavy Cavalry still some hours behind the main body. Napoleon decided that he would posture as a weak force to encourage the Austrians to stand and fight, he would attack once Davout arrived and order him to attack from his line of march. Napoleon’s intent was to drive the Austrians into the ISAR. By destroying two or three AK he might end the war on the 23rd April.
The Austrian Corps Commanders conference, over breakfast, on the 23rd was a heated and angry debate. There were strong arguments to withdraw as soon as possible. However, the fear was that the French were too close and could easily push the majority of the Corps into the ISAR, and destroy a large portion of the combined Austrian Force. Even worse there could be panic and they could lose control of all their forces. The senior Austrian Commander, FZM Kolowrat-Krakowsky commanding the 2nd AK, prevailed in the debate and directed that the combined forces stand and fight for the road south east to clear of the baggage and then for the forces to withdraw over the bridge. His colleagues were uncomfortable with the decision but decided to abide by his recommendation. The die was cast.
Battlefield Map and Terrain
Around the banks of the rivers in Bavaria the ground is relatively flat with the occasional minor elevation. There are frequent small villages, these provide some cover and security around which a defence can be built. The road to the south led to a bridge over the River ISAR. North and East are bounded by the River DANUBE.
The Battle
At 10:00hrs the Austrian 1st AK is deployed in line of battle. On the left the 3rd Div 2nd AK is in support with its Jagers and IR25 securing the end of the line in the village of PLAUING. Similarly the 3rd Div 1st AK were securing the right around the village of ISARGMUND. The VII (Bav) CA are arrayed in a cordon to secure the line of departure for III Corps D’Armee’s attack.
By 11:00hrs the French attach was starting to develop led by the 3rd (Bav) Div attacking the Jagers in the wood west of PLAUING. They were supported in this attack by the massed batteries of the 3rd and 1st Div.
As a result of the Bavarian assault on the woods the Jagers withdrew through the wood supported by IR25 which was suffering from the artillery fire directed at it. CLR5 moved up in support to cover the withdrawal of the 3rd Div into line with the 1st AK.
By 11:30hrs the 2nd AK had reversed its march and was arriving to support the 1st AK. However, for the French III CA was starting to arrive. The 1st (Bav) Div remained on its start line to the rear of the hill North of PLAUING, the intention to be for this to move up once the 2nd(BAV) Div moved on to their left flank.
An hour later 2nd AK was starting to deploy to the left of 1st AK. For the French the 2nd (Bav) Div was now starting to approach its start line to allow the combined Bavarian attack to start. In the north the III CA is continuing to move forward in column of march to the East with the intention of swinging to the South to attack along the line of the road running from KLEINKUCHIG-ISARGMUND-the crossing over the ISAR.
Outside PLAUING the 3rd (Bav) Div is regrouping while the Austrian 3rd Div of the 2nd AK withdraws to its main body.
At 1300hrs the Austrians are starting to change their dispositions. The arrival of the 2nd AK has allowed the 1st AK to shorten its line. The 3rd Div 1st AK has thrown its Jagers forward as a screen in the woods North West of ISARGMUND.
The VII (Bav) CA started its advance with its 1st and 2nd Div at 1330. The advance guard of the III CA has evicted the Jager screen that was sent forward and is moving in support of the Bavarians. Both Austrian Corps Commanders have assembled a strong reserve e to counterattack any breakthroughs made by the French, and also to act as line through which the forward units can withdraw.
By 1330hrs the French now have four divisions in a line all directed at the two and a half divisions of the 1st AK.
By 1500hrs the French attack has made significant progress. III CA has passed through the 1st (Bav) Div and has pushed the Austrian Centre into retreat. In doing so it has opened a gap between the 1st and 2nd AK. This French attack has exposed the left and right flanks of the Austrian position, although they are both continuing to give a good account of themselves in their own fights. Meanwhile the Austrian commanders have decided to save the guns and to extract them from the battle and across the ISAR. The 2nd Hvy Cav Division, which arrived at 1200hrs, were rushed forward by Napoleon and they joined the attack to try and complete the victory.
From 1500hrs the French launch charges all along the line driving the Austrians into ever more confusion and fragmentation. The Austrian defensive fire cannot stop the French momentum.
The French charges force the Austrians into an ever-tighter perimeter. Notably Brigade Destabenrath of St Hilaire’s Division has penetrated deep into the Austrian position to cause major disruption. A number of Austrian units are left effectively surrounded as the French penetrate into the depths of the Austrian Line. There is the start of massive congestion as troops hasten their exit from the battlefield.
In order to stabilise the line and to buy time for retreat IR15 launched a partially successful counterattack to drive back Brigade Destabenrath. While IR18 form square to defend themselves against the Cuirassiers. With the decreasing Austrian perimeter there is insufficient space to allow Napoleon to bring his whole force and strength to bear on the Austrians.
Despite the French success at 1530hrs the Austrians manage to secure the initiative and troops flood to the rear to cross the bridges over the ISAR. There remains a paltry rearguard of Austrians who sacrifice themselves to allow the rest of their two AK to withdraw and preserve their remaining strength for future battles
Outcome and Casualties
Although the battle was a major defeat for the Austrians, it was not the stunning victory that Napoleon sought. The Austrians were able to extricate a significant portion of their forces. Although both Armee Korps were depleted they made good their escape. Significantly only one Austrian battery was lost. Strategically the French were now forced into chasing the Austrians along the Danube in an attempt to overtake them and bring them to battle again.
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